In recent years, solid light sources such as LEDs (Light Emitting Diodes) are utilized for lighting. This sort of solid light source can be lit with a lighting device.
An LED dimmer known as such a lighting device includes a current adjusting means, a switch means and a dimming control means (for example, JP Pub. No. 2009-123681 (hereinafter, referred to as “Document 1”)). The current adjusting means adjusts a current amount with respect to an LED load. The switch means operates to cause a (an electric) current to intermittently flow through the LED load. The dimming control means controls the current adjusting means and the switch means.
The LED dimmer of Document 1 has a dimming function that receives a dimming signal from a dimmer controller to adjust a light output (an optical output) of the LED load. When the dimming signal represents a level corresponding to brightness higher than a predetermined level (a high brightness side), the LED dimmer changes a current flowing through the LED load to a continuous current. In the case of the high brightness side, the LED dimmer adjusts the light output of the LED load by changing the current amount with respect to the LED load. When the dimming signal represents a level corresponding to brightness lower than the predetermined level (a low brightness side), the LED dimmer changes the current flowing through the LED load to a pulsed current. In the case of the low brightness side, the LED dimmer adjusts the light output of the LED load by changing a mean value of the pulsed current waveform.
This sort of lighting device requires adjusting a light output of its own solid light source at a lower luminous flux. Thus, the LED dimmer described above needs to be further improved.